Preterm Birth and Stressful Life Events

Preterm Birth
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  Chapter 2 Preterm Birth and Stressful Life Events Susan Cha and Saba W. Masho Additional information is available at the end of the chapter 1. Introduction Stress is defined as a physiologic response to psychological and physical demands and threats[1]. That is - when “environmental demands tax or exceed the adaptive capacity of an organism,resulting in psychological and biological changes that may place persons at risk for disease”[2]. Despite the challenges of measuring, defining, and studying stress, a large body ofliterature documents the contributions of stressors and affective state during pregnancy on birth outcomes [3]. In the last two decades, psychosocial stress has evolved to encompassmental health states and stressors such as anxiety, depression, racism, lack of social support,coping mechanisms, job strain, acculturation stress, and domestic violence [4].In general stress is divided into acute and chronic stress. While stress may have some benefitsin responding to stressors, chronic stress has been shown to be associated with chronic diseasesincluding preterm birth. Acute stress is short-lived, an effective resolution to heightenedthreats or demands [1]. Examples of acute stresses can be impending final exams for collegestudents, brief relationship arguments, and minor upsets in finances. Chronic stress persistsfor longer period of time without resolution to threats or demands. Stressors that accompanysocial racism, prolonged homelessness, living in sub-standard conditions, living in high crimerate neighborhoods, and being a single parent are long-standing and chronic.Mounting evidence has linked stress to multiple chronic diseases over the years. This isparticularly true in studies investigating preterm births. Preterm birth is one of the leadingcauses of infant mortality and childhood morbidities and it is mainly caused by prematurerupture of membrane. Although some of the factors leading to premature births are known,the cause for early labor is not fully understood. In the past decade, the influence of stress onpremature birth has received special attention. This chapter discusses the role of stress as itrelates to preterm birth. Additionally, the patho-physiologic mechanisms, risk factors, andpsychometric measures and biomarkers used to assess stress are examined. © 2013 Cha and Masho; licensee InTech. This is an open access article distributed under the terms of theCreative Commons Attribution License (, which permitsunrestricted use, distribution, and reproduction in any medium, provided the srcinal work is properly cited.  2. Poor birth outcomes and stress Preterm and low birth weight, and intrauterine growth restriction are the leading causes ofneonatal and infant morbidity, mortality, and neurodevelopmental impairments worldwide[5,6]. A preterm birth is the birth of an infant less than 37 weeks of gestation. Preterm birthcontributes to other adverse birth outcomes such as low birth weight (defined as 2,500 gramsor less), developmental delays, infections and cognitive impairment [7]. An extensive body of research provides evidence for the relationship between stress and poor birth outcomes suchas prematurity and low birth weight. Other adverse health sequelae such as birth defects,miscarriages, stillbirth, and maternal complications (i.e. preeclampsia, gestational diabetes,and prenatal hemorrhaging) are also associated with maternal stress [8-11]. Occurring in 8 to12 percent of all pregnancies worldwide, rates of preterm birth and low birth weight are higherin the United States compared to other industrialized nations [12]. Despite efforts to improve birth outcomes, preterm birth and low birth weight remain a major issue due to increasingdisparities in rates [13]. Moreover, certain subgroups are disproportionately affected by theproblem. For instance, in the U.S., African-Americans have almost twice the rate of low birthweight and preterm delivery, and three times the rate of very low birth weight (<1,500 grams)and very preterm delivery (<32 weeks) compared to Caucasian Americans [14]. High rates ofprematurity and low birth weight are of public health concern because they are the leadingcauses of infant and neonatal morbidity and mortality [15]. Preterm infants are at higher riskfor serious complications such as respiratory, gastrointestinal, nervous system, and immune-related problems [7]. 2.1. Preterm birth The first study to explore the relationship between stress during pregnancy and development biology took place in the 1940’s with the advent of Sontag’s pioneering work [16]. Sontagobserved a relationship between emotional disturbance in pregnant mothers and hyperactivefetuses and early feeding difficulties in their offspring. More than two decades later, Gunterpublished a report on stressful environmental and psychological factors before and duringpregnancy and preterm birth among Afro-American women [17]. Twenty cases of women whoexperienced preterm birth were matched with 20 women with normal deliveries. Gunterconducted a thorough evaluation using a battery of assessments that included measures ofself-concept, psychosomatic and neuropsychiatric symptoms, and life events related to deathin the family, desertion, economic need, and physical disabilities. Results implied a relation‐ship between psychosomatic conditions and life or social situation of the mother were relatedto the outcome of pregnancy. Until the 1990’s, many investigations on stress and preterm birthwere largely retrospective, riddled with weak conceptualizations and methodological problems that limited conclusions [18]. Since then, the body of research on psychosocial stressand preterm has grown substantially, and though there are conflicting reports, studies haveshown that women experiencing high stress are 1.5 to 3 times more likely to experience pretermdelivery than less distressed women [7,19,20]. Preterm Birth42  Dole and colleagues conducted a study to examine a comprehensive panel of psychosocialfactors among which included negative life events, pregnancy-related anxiety, and otherstressors in relation to preterm birth in a prospective cohort study of nearly 2,000 pregnantwomen in North Carolina [21]. They found that women in the highest negative life eventsimpact quartile had the highest risk of preterm birth (adjusted RR = 1.8, 95% CI = 1.2 to 2.7).Further, pregnancy-related anxiety in mid-pregnancy predicted spontaneous preterm birtheven after controlling for a wide range of confounding variables (RR = 2.0, 95% CI = 1.6 to 3.9).There is converging evidence across studies of diverse populations regarding the adverseeffects of pregnancy anxiety on preterm birth [3]. Pregnancy anxiety, defined as fears andanxiety related to the health and well-being of the ba by , childbirth, and postpartum parenting,predicts the risk of spontaneous preterm birth with consistent results for various racial andethnic groups [3,22].Dunkel Schetter and Glynn conducted a systematic review for the relationship betweenvarious types of stress and preterm birth [23]. This comprehensive study included more than80 studies of which most had prospective designs with robust sample size and validatedmeasures. Authors reported that stressful life events, major community-wide disasters,chronic stressors, and pregnancy anxiety increased the risk for preterm birth. Of the studiesassessing major life events during pregnancy, more than half reported significant effects ongestational age or preterm birth. Women who experienced stressful life events such as thedeath of a family member were 1.4 to 1.8 times as likely to have a preterm birth. Similar toother studies, the estimate of effect was stronger when stressful life events took place earlierin the pregnancy. Other types of stress brought on by natural disasters or terrorist attacks, chronic strain (i.e. general, household, homelessness), and neighborhood stressors (such aspoverty and crime) also contributed independently to the risk of preterm birth or gestationalage. Although studies that used standard scales to measure daily hassles showed no significanteffect on birth outcomes, using combinations of perceived stress measures predicted preterm birth in some studies [15,24,25].Two main factors have emerged as central in better understanding the impact of life eventstressors on preterm birth: timing of stressor and self-perceived stress [26]. Several studieshave shown a decline in psychological and physiological stress response in pregnant womenas pregnancy progresses [27-30]. A paper published in 2001 by Glynn and colleagues reportedthat women who lived through the Northridge earthquake in California showed a differentialresponse to the psychological effect of the earthquake depending on their gestational age atthe time of the event [28]. There was a significant association between women who experiencedthe stress early in the pregnancy and shorter gestational age at delivery. Participants in thefirst trimester also evaluated the earthquake as more upsetting and aversive than women inthe second or third trimester scoring higher on a life events inventory. Similar results were observed among women who lived through the aftermaths of the terrorist attacks at the WorldTrade Center on September 11, 2001 [31]. Women who were in their first trimester at the timeof the stressful incident showed shorter gestational times than controls; however no differencewas observed among women in the second trimester. Considering the time frame of maternal Preterm Birth and Stressful Life Events  exposure to stress and self-perceived severity of stress may be important in understandinghow women’s response to stress has an impact on fetal development. 2.2. Low birth weight Chronic stressors are robust predictors of low birth weight, infant weighing less than2,500 grams at birth [32]. Although a significant proportion of low birth weight infantsare preterm births, several studies have reported the impact of stress on low birthweight. A recent population-based cohort study conducted by Brown et al. sought to ex‐amine the social determinants of low birth weight in Australia [20]. One in six women re‐ported three or more stressful life events or social health issues in the 12 monthspreceding the last birth. Women coping with multiple life events remained significantlymore likely to have a low birth weight infant after adjusting for smoking, number of pre‐natal visits, and other known covariates. Specifically, women reporting three or morestressful events or social health issues had a twofold increase in odds of having a low birth weight infant compared to women reporting no issues. In a U.S. study, maternalstress was associated with 2 to 3.8 times the risk of low birth weight among a sample ofnearly 1,400 pregnant low-income women [33]. In fact, there is a 55-gram reduction in in‐fant birth weight or low birth weight for every unit increase of stressful life event [34].Similar results have been observed elsewhere in European countries [35-37].In Amsterdam, Paarlberg et al. recruited almost 400 women from several obstetric outpatientclinics to conduct a prospective study on stressors and low birth weight [36]. Questionnaireson daily stressors, psychological and mental well-being, and social support were completed by women throughout their pregnancy. Having experienced daily stressors in the firsttrimester was associated with an increased risk of low birth weight. Indeed the relationshipwas strongest when multiple exposures interacted to contribute to a compromised fetalgrowth. In Scotland expectant mothers perceiving high levels of household stress at 20 weeksgestation had increased odds of low birth weight (OR = 4.7, 95% CI = 1.5 to 13.4) [35]. Resultsfrom the Scotland study suggests that the relationship between psychosocial stress and low birth weight may be attributable to variation in energetic intake and expenditure. For example,pregnant women who carry the burden of running a household without the support of ahusband or partner may suffer inadequate nutritional provisioning and greater workload,reducing maternal and fetal weight gain.Overall, preterm birth and low birth weight are commonly studied together as tandemoutcomes because infants born preterm are often of low birth weight. It has been estimatedthat two-thirds of low birth weight infants are born preterm [3]. Prior work in the field hadthe tendency to combine various psychological processes into one psychosocial category thattypically consisted of stress, emotions, coping, social support, and more. However, a growing body of research supports differences in the psychological processes involved in the etiologyof both birth outcomes [23,25]. While pregnancy anxiety appears to be a strong predictor ofpreterm birth, depression and chronic strain appear to be stronger predictors of low birthweight [23]. Epidemiologic and social behavioral studies on the psychological pathwayscontributing to these two birth outcomes deserve individual attention. Disentangling the Preterm Birth44
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